Cladding Process for Blower Impeller Blades in Sintering Operations

Overview of the Literature

This technical note addresses the weld overlay (cladding) technology applied to blower impeller blades used in sintering operations, published in 1989 by Zhao Jiancang. Sintering blowers operate under extremely harsh conditions involving abrasive dust, high temperatures, and continuous mechanical vibration. The impeller blades, which are the most critical wear components of the blower, typically suffer from abrasive erosion, impact wear, and thermal fatigue. The original literature describes the selection of cladding processes and filler materials specifically tailored to extend blade service life in this demanding environment.

Core Technical Content

Service Conditions and Failure Analysis

Sintering blowers in iron and steel plants handle hot, abrasive gas streams containing fine particulate matter at temperatures ranging from 200°C to 450°C. The blade surfaces are subjected to a combination of:

• Abrasive wear from solid particles impacting at velocities of 30–80 m/s
• Thermal cycling causing fatigue cracks at the blade root
• Corrosive attack from sulfur-bearing gases in the sintering process
• Mechanical vibration from centrifugal loading at rotational speeds of 1200–2400 rpm

The baseline blade material is typically a medium-carbon steel or low-alloy steel (such as 45 steel or 16Mn), which provides adequate strength but insufficient wear resistance for prolonged service.

Cladding Process Selection

The literature discusses several cladding approaches evaluated for this application:

For impeller blades, the key challenge is the thin cross-section and complex geometry. The literature indicates that a combination of SMAW for base buildup and FCAW or SAW for the final wear-resistant layer is most practical in industrial settings of that era.

Filler Material Selection

The critical technical decision involves selecting the appropriate cladding alloy. The literature evaluates several categories:

For sintering blower blades, the literature recommends a layered approach: a transition layer of austenitic stainless steel (such as 309L equivalent) to ensure weldability with the base steel, followed by 2–3 passes of a high-chromium martensitic or Fe-based hardfacing alloy.

Process Parameters and Technical Details

Pre-Weld Preparation

• Surface grinding to remove scale, rust, and previous weld defects
• Edge preparation with 60° included angle V-groove for thick cladding
• Preheating at 150–250°C for base steels with carbon equivalent > 0.4%
• Flux deoxidation and drying according to manufacturer specifications

Welding Parameters (Typical for FCAW Cladding)

Post-Weld Treatment

• Stress relief annealing at 600–650°C for 1–2 hours to reduce residual stresses
• Controlled cooling in furnace to prevent microcracking in martensitic layers
• Surface finishing to achieve required aerodynamic profile (Ra ≤ 12.5 μm)

Engineering Practice and Defect Control

Common Defects and Countermeasures

Performance Verification

After cladding, the following tests should be performed:

1. Hardness testing — Vickers or Rockwell C, verifying ≥ 50 HRC for the outermost layer
2. Impact test — Charpy V-notch at room temperature, verifying ≥ 27 J for transition layer
3. Metallographic examination — 100× magnification to check for cracks, segregation, and proper layer bonding
4. Bond strength test — Peel test or torsion test per ASTM G141 or equivalent
5. Dimensional check — Profile verification using coordinate measurement or optical comparison

Study Insights and Reflections

This 1989 publication represents an important early Chinese contribution to the practical application of cladding technology in the sintering industry. The approach described — using a multi-layer strategy with a transition layer — reflects sound metallurgical thinking that remains valid today. The emphasis on balancing wear resistance with thermal stability is particularly noteworthy, as many early cladding applications focused solely on hardness without considering the thermal environment.

One critical insight from this literature is the recognition that impeller blade cladding is not merely a surface treatment but a structural modification requiring careful consideration of the blade root stress concentration. The blade root, where the highest bending stresses occur, should not be over-cladded, as excessive buildup can alter the stress distribution and potentially initiate fatigue failure. The recommended practice is to apply the wear-resistant layer primarily to the leading edge and pressure side surface, while maintaining a thin, tough transition layer at the root.

The process parameters described, while typical of the late 1980s, provide a useful baseline for understanding the evolution of cladding technology. Modern practices would likely employ laser cladding or PTA for superior dilution control, but the fundamental metallurgical principles — layer selection, preheat, stress relief — remain unchanged.

Practical Recommendations

For engineers currently working on blower impeller cladding in sintering or similar abrasive environments:

• Always perform a detailed failure analysis before selecting cladding materials
• Consider the full operating temperature cycle, not just peak temperature
• Use metallographic cross-section examination to verify layer integrity after production
• Establish a cladding qualification procedure per NB/T 47014 or ASME IX Section IX, QW-400 series
• Maintain records of field service life to enable continuous improvement of material and process selection

The literature's practical orientation and focus on industrial applicability make it a valuable reference for engineers seeking to understand the foundational principles of wear-resistant cladding in rotating machinery applications.